1. Field of the Invention
The present invention relates to a hard disk drive (HDD). More particularly, the present invention relates to means for controlling movement of a head stack assembly which includes the read/write head of the HDD.
2. Description of Related Art
Hard disk drives (HDDs) are devices which can quickly access large amounts of data. Thus, HDDs have been widely used for a long time as auxiliary memory devices of computers. In general, an HDD includes a disk on which data is/can be stored, and a read/write head that records data on the disk or reproduces data stored on the disk. In this respect, units of the data, in the form of bits, are magnetically recorded on or reproduces from tracks of the disk.
The data storage disks for use in HDDs are continuously being improved to increase the TPI (tracks per inch) and BPI (bits per inch). These and other improvements have led to more compact HDDs and have thus expanded the number of electronic products which employ an HDD as a memory device. In particular, compact HDDs are now employed by portable electronic products such as laptops, personal digital assistants (PDAs), and mobile phones. The disk of a typical compact HDD has a diameter of 2.5 inches. However, disks as small as 0.8 inches in diameter, i.e., whose size is similar to that of a coin, are been actively developed for use in mobile phones or MP3 players.
FIG. 1 is a plan view of a conventional compact HDD 101. Referring to FIG. 1, the HDD 101 includes a disk pack 110 having a disk 111, a head stack assembly (HSA) 140 having a read/write head 141 for recording data on the disk 111 and reproducing data from the disk 111, a voice coil motor (VCM) for driving the HSA 140, a latch 170 for preventing the read/write head 141 from moving across the disk 111 when the HDD is in a non-operating state, a ramp 180 on which the read/write head 141 of the HSA 140 is parked while the HDD is in the non-operating state, and a 160 to which the above-mentioned elements are mounted, and a cover (not shown).
In addition to the read/write head 141, the HSA 140 includes an actuator arm 143 having a distal end at which the read/write head 141 is supported, a pivot 142 in the form of a shaft fixed relative to the base 160, and a pivot holder 144 supported by the pivot 142 so as to be rotatable about the central longitudinal axis of the pivot 142. The actuator arm 143 is coupled at a proximate end thereof to the pivot holder 144 so as to be rotatable therewith. Therefore, the read/write head 141 can be moved across the disk 111 by rotating the actuator arm 143 about (the central longitudinal axis of) the pivot 142.
The HSA 140 also includes a bobbin 145 integral with and extending from the proximate end of the actuator arm 143, i.e., from the side of the pivot holder 144 opposite that from which the actuator arm 143 generally extends. A voice coil 146 of the VCM 130 is wound around the bobbin 145, and a VCM block of the VCM 130 is installed on the base 160. The VCM block includes a magnet 132 that is juxtaposed with the voice coil 146. The actuator arm 143 is rotated by an electromagnetic force generated between the voice coil 146 and the magnet 132 when current flows through the voice coil 146. Bobbin pins provided on the pivot holder 144 to connect a flexible printed circuit board (FPCB) to the voice coil 146 winding along the bobbin 145. The FPCB is, in turn, electrically connected to a PCB (not shown) disposed below the base 160 and configured to control the VCM.
According to the functions described above, the read/write head 141, supported at the distal end of the actuator arm 143, is positioned by the VCM over a track of the disk 111 to record data on the disk 111 or reproduce data from the disk 111. However, before this happens, the bobbin 145 must be released by the latch 170.
That is, the latch 170 hooks onto the bobbin 145 when the HDD is in its non-operating state. To this end, a retract pin 148 is disposed on a protruding portion 147 of the bobbin 145 that is hooked by the latch 170. The retract pin 148 is of a magnetic material and acts with the magnet 132 of the VCM 130 to generate a force which urges the bobbin 145 to rotate in direction A in FIG. 1, i.e., toward the latch 170. In this state, as mentioned above, the distal end of the actuator arm 143 rests on the ramp 180, and the read/write head 141 is said to be “parked” on the ramp 180. The engagement between the bobbin 145 and the latch 170 prevents the read/write head 141 from moving away from the ramp 180 and onto the disk 111 even when an external shock is applied to the HDD. Thus, the latch 170 serves to prevent the read/write head 141 and/or the recording surface of the disk 111 from being damaged when the HDD is in its non-operating state.
In the conventional HDD 101 as described above, the function of the latch 170 may be adversely affected due to warping of the bobbin 145 and/or if the base 160 is not level relative to the HSA 140. The bobbin 145 is likely to warp because the retract pin 148 is fixed the very end of the bobbin 145, i.e., because the retract pin 148 which is attracted towards the magnet 132 is located relatively far from the fixed axis (pivot 142) of the HSA 140. Such factors (warpage of the bobbin, etc.) can cause the actual distance between the bobbin 145 and the magnet 132 of the VCM to deviate from the distance specified according to the design of the HDD. In this case, a force that is greater than or less than the predetermined (design) force specified for the latch 170 to operate properly may be generated. For instance, the read/write head 141 may not be moved toward the disk 111, at the start of a read/write operation, when the actual force generated between the retract pin 148 and the magnet 132 is greater than the predetermined force.
On the other hand, the read/write head 141 can be moved onto the disk 111 by an external shock if the actual force generated between the retract pin 148 of the latch and the magnet 132 of the VCM is less than the predetermined force. Furthermore, the magnetic field generated between the magnet 132 and the retract pin 148 must not affect a magnetic region of the disk 111, which is of a concern because the protruding portion 147 of the bobbin 145 to which the retract pin 148 is mounted is swung toward the disk 111 when the read/write head 141 is being parked. This concern associated with the provision of the retract pin 148 imposes limits on the size of the magnet 132 of the VCM. Limiting the size of the magnet 132 also limits the electromagnetic force which can be generated by the VCM for rotating the actuator arm 143.